Different types of ink jet printers form their droplets of ink employing different methods. There are several technologies used by printer manufacturers, one of the most popular of which is the thermal ink jet. In a thermal ink jet printer, small resistors create heat which vaporizes ink to create a bubble adjacent to a print nozzle. The expansion that creates the bubble causes a droplet of ink to be ejected from the nozzle onto the media. Other technologies include piezo elements to generate pressure waves which cause drop ejection.
Ink jet type printers typically employ a printhead cartridge which is moved in a transverse fashion across a print media. Contemporary disposable ink jet printhead cartridges typically include a pen body with a self-contained ink reservoir, a printhead supporting a plurality of ink jet nozzles in combination with the ink reservoir, and a plurality of external electrical contacts for connecting the ink jet nozzles to driver circuitry. For a printer of this type there may be hundreds of these nozzles on the printhead. Printhead failure is usually due to failure of the resistors used to heat the ink in proximity to each nozzle. Due to relatively low resistor failure rates, the printhead used in the currently available disposable ink jet cartridges are fully operable to their original print quality specifications after the original ink reservoir has been depleted.
The disposal of these ink jet cartridges which are still able to perform adequately, except for the lack of ink in their supply containers, is wasteful. As a result, it is known in the art to manually replenish the ink reservoir within the disposable ink jet cartridge. However, manually refilling the disposable ink cartridges is often messy and difficult because many disposable ink jet cartridges are not designed with refilling in mind.
Furthermore, the back pressure at the printhead should be large enough to prevent the undesired free flow of ink through the nozzles when the printhead cartridge is at rest. The back pressure should also be small enough so that the printhead can overcome the back pressure and eject ink droplets in a consistent and predictable form when printing. What is needed is an improved printhead cartridge with a replaceable ink supply tank that is easy and clean to replace, yet maintains the appropriate back pressure desired for consistent printhead performance.